BIND 10 #1568: Change throw to assert to gain performance

[BIND 10 Development]

#1568: Change throw to assert to gain performance
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                   Reporter:         |                 Owner:  jinmei
  vorner                             |                Status:  reviewing
                       Type:         |             Milestone:
  enhancement                        |  Sprint-20120320
                   Priority:         |            Resolution:
  medium                             |             Sensitive:  0
                  Component:         |           Sub-Project:  DNS
  b10-auth                           |  Estimated Difficulty:  0
                   Keywords:         |           Total Hours:  0
            Defect Severity:  N/A    |
Feature Depending on Ticket:         |
  performance                        |
        Add Hours to Ticket:  0      |
                  Internal?:  0      |
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Comment (by jinmei):

 Now the new `MessageRenderer` implementation is likely to need this,
 I think it's time to resume this ticket.

 First, I made a very minor editorial fix to the branch.

 Second, I think we need a changelog for this because it could
 potentially change observable behavior.

 Third, I wonder we could do something similar to what I did in
 trac1603: still throw on error but move the throw statement to a
 separate private method:
 {{{#!diff
 -        assert(pos < size_);
 +        if (pos >= size_) {
 +            throwError();
 +        }
          return (buffer_[pos]);
      }
      //@}
 +private:
 +    static void throwError() {
 +        isc_throw(InvalidBufferPosition, "read at invalid position");
 +    }
 +public:
 }}}

 I've tested this on trac1603bench, and I saw it was slightly slower
 than the assert() version, but the gap was not that big and I was not
 sure if it was an experimental margin or the real difference due to
 the implementation difference.  At the moment I'm okay with keeping
 the use of assert() if we want the highest possible performance, but
 we might note the possibility of future extension where we use an
 exception in a separate function.

 Other than these, the branch is okay for merge.

-- 
Ticket URL: <http://bind10.isc.org/ticket/1568#comment:6>
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